1. Field of the Invention
The present invention relates to a vapor deposition apparatus used for producing semiconductors, and particularly to a vapor deposition apparatus for efficiently producing a thin film or particles with use of light energy.
2. Description of the Prior Art
An optical CVD method uses light energy of a laser beam or of light of a lamp to form a thin film on a substrate.
FIG. 1 is a sectional view showing an example of a conventional vapor deposition apparatus employing the optical CVD method.
This apparatus comprises a reaction tube 100. The reaction tube 100 incorporates a substrate 101, a substrate holder 102 for holding the substrate 101, and a high-frequency coil 103 for heating the substrate 101 and substrate holder 102. A gas inlet 100a is formed at the top of the reaction tube 100, to introduce a material gas of, for example, Si.sub.2 H.sub.6 and a carrier gas of, for example, H.sub.2 into the reaction tube 100. An outlet 100b is formed at the bottom of the reaction tube 100, to discharge an unreacted gas, etc., outside the reaction tube 100.
A transparent window 104 made of, for example, quartz, is formed at a side face of the reaction tube 100 between the gas inlet 100a and the substrate 101. An optical system 105 and a laser 106 serving as a light source are disposed outside the window 104.
The material gas is introduced into the reaction tube 100 through the gas inlet 100a. The laser 106 emits a laser beam, which enters the reaction tube 100 through the optical system 105 and window 104 and irradiates the material gas. The material gas absorbs the laser beam and decomposes to deposit as a thin film on the substrate 101.
Since the laser 106, i.e., a laser resonator of this conventional vapor deposition apparatus is outside the reaction tube 100, energy of the laser beam entered into the reaction tube 100 through the window 104 drastically attenuates to about one hundredth of that of the laser beam produced inside the laser resonator. In this way, energy of a laser beam extremely attenuates once it comes out of the laser resonator.
In addition, the diameter of the laser beam is too small to decompose the material gas to form a quality thin film.